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A vitamin is an organic compound required as a nutrient in tiny amounts by an organism. A compound is called a vitamin when it cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. Thus, the term is conditional both on the circumstances and the particular organism. For example, ascorbic acid functions as vitamin C for some animals but not others, and vitamins D and K are required in the human diet only in certain circumstances.
Vitamins are classified by their biological and chemical activity, not their structure. Thus, each "vitamin" may refer to several vitamer compounds that all show the biological activity associated with a particular vitamin. Such a set of chemicals are grouped under an alphabetized vitamin "generic descriptor" title, such as "vitamin A," which includes the compounds retinal, retinol, and many carotenoids. Vitamers are often inter-converted in the body. The term vitamin does not include other essential nutrients such as dietary minerals, essential fatty acids, or essential amino acids, nor does it encompass the large number of other nutrients that promote health but are otherwise required less often.
Vitamins have diverse biochemical functions, including function as hormones (e.g. vitamin D), antioxidants (e.g. vitamin E), and mediators of cell signaling and regulators of cell and tissue growth and differentiation (e.g. vitamin A). The largest number of vitamins (e.g. B complex vitamins) function as precursors for enzyme cofactor bio-molecules (coenzymes), that help act as catalysts and substrates in metabolism. When acting as part of a catalyst, vitamins are bound to enzymes and are called prosthetic groups. For example, biotin is part of enzymes involved in making fatty acids. Vitamins also act as coenzymes to carry chemical groups between enzymes. For example, folic acid carries various forms of carbon group – methyl, formyl and methylene - in the cell. Although these roles in assisting enzyme reactions are vitamins' best-known function, the other vitamin functions are equally important.
Until the 1900s, vitamins were obtained solely through food intake, and changes in diet (which, for example, could occur during a particular growing season) can alter the types and amounts of vitamins ingested. Vitamins have been produced as commodity chemicals and made widely available as inexpensive pills for several decades, allowing supplementation of the dietary intake.
- 1 History
- 2 In humans
- 3 In nutrition and diseases
- 4 Supplements
- 5 Names in current and previous nomenclatures
- 6 See also
- 7 References
- 8 External links
The value of eating a certain food to maintain health was recognized long before vitamins were identified. The ancient Egyptians knew that feeding a patient liver would help cure night blindness, an illness now known to be caused by a vitamin A deficiency. The advancement of ocean voyage during the Renaissance resulted in prolonged periods without access to fresh fruits and vegetables, and made illnesses from vitamin deficiency common among ship's crew.
In 1881, Russian surgeon Nikolai Lunin studied the effects of scurvy while at the University of Tartu in present-day Estonia. He fed mice an artificial mixture of all the separate constituents of milk known at that time, namely the proteins, fats, carbohydrates, and salts. The mice that received only the individual constituents died, while the mice fed by milk itself developed normally. He made a conclusion that "a natural food such as milk must therefore contain, besides these known principal ingredients, small quantities of unknown substances essential to life." However, his conclusions were rejected by other researchers when they were unable to reproduce his results. One difference was that he had used table sugar (sucrose), while other researchers had used milk sugar (lactose) that still contained small amounts of vitamin B.
|Year of discovery||Vitamin||Source|
|1909||Vitamin A (Retinol)||Cod liver oil|
|1912||Vitamin B1 (Thiamin)||Rice bran|
|1912||Vitamin C (Ascorbic acid)||Lemons|
|1918||Vitamin D (Calciferol)||Cod liver oil|
|1920||Vitamin B2 (Riboflavin)||Eggs|
|1922||Vitamin E (Tocopherol)||Wheat germ oil, and Liver|
|1926||Vitamin B12 (Cyanocobalamin)||Liver|
|1929||Vitamin K (Phylloquinone)||Alfalfa|
|1931||Vitamin B5 (Pantothenic acid)||Liver|
|1931||Vitamin B7 (Biotin)||Liver|
|1934||Vitamin B6 (Pyridoxine)||Rice bran|
|1936||Vitamin B3 (Niacin)||Liver|
|1941||Vitamin B9 (Folic acid)||Liver|
In east Asia, where polished white rice was the common staple food of the middle class, beriberi resulting from lack of vitamin B was endemic. In 1884, Takaki Kanehiro, a British trained medical doctor of the Japanese Navy, observed that beriberi was endemic among low-ranking crew who often ate nothing but rice, but not among crews of Western navies and officers who consumed a Western-style diet. Kanehiro initially believed that lack of protein was the chief cause of beriberi. With the support of the Japanese navy, he experimented using crews of two battleships; one crew was fed only white rice, while the other was fed a diet of meat, fish, barley, rice, and beans. The group that ate only white rice documented 161 crew members with beriberi and 25 deaths, while the latter group had only 14 cases of beriberi and no deaths. This convinced Kanehiro and the Japanese Navy that diet was the cause of beriberi. This was confirmed in 1897, when Christiaan Eijkman discovered that feeding unpolished rice instead of the polished variety to chickens helped to prevent beriberi in the chickens. The following year, Frederick Hopkins postulated that some foods contained "accessory factors"—in addition to proteins, carbohydrates, fats, et cetera—that were necessary for the functions of the human body. Hopkins was awarded the 1929 Nobel Prize for Physiology or Medicine with Christiaan Eijkman for their discovery of several vitamins.
In 1910, Japanese scientist Umetaro Suzuki succeeded in extracting a water-soluble complex of micronutrients from rice bran and named it aberic acid. He published this discovery in a Japanese scientific journal.
When the article was translated into German, the translation failed to state that it was a newly discovered nutrient, a claim made in the original Japanese article, and hence his discovery failed to gain publicity. Polish biochemist Kazimierz Funk isolated the same complex of micronutrients and proposed the complex be named "Vitamine" (a portmanteau of "vital amine") in 1912. The name soon became synonymous with Hopkins' "accessory factors", and by the time it was shown that not all vitamins were amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped to deemphasize the "amine" reference after the discovery that vitamin C had no amine component.
Throughout the early 1900s, the use of deprivation studies allowed scientists to isolate and identify a number of vitamins. Initially, lipid from fish oil was used to cure rickets in rats, and the fat-soluble nutrient was called "antirachitic A". Thus, the first "vitamin" bioactivity ever isolated, which cured rickets, was initially called "vitamin A", although confusingly the bioactivity of this compound is now called vitamin D. What we now call "vitamin A" was identified in fish oil as a separate factor that was inactivated by ultraviolet light. In 1931, Albert Szent-Györgyi and a fellow researcher Joseph Svirbely determined that "hexuronic acid" was actually vitamin C and noted its anti-scorbutic activity. In 1937, Szent-Györgyi was awarded the Nobel Prize for his discovery. In 1943 Edward Adelbert Doisy and Henrik Dam were awarded the Nobel Prize for their discovery of vitamin K and its chemical structure.
Vitamins are classified as either water-soluble or fat soluble. In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C).
Water-soluble vitamins dissolve easily in water, and in general, are readily excreted from the body, to the degree that urinary output is a strong predictor of vitamin consumption. Because they are not readily stored, consistent daily intake is important. Many types of water-soluble vitamins are synthesized by bacteria.
Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Because they are more likely to accumulate in the body, they are more likely to lead to hypervitaminosis than are water-soluble vitamins. Fat-soluble vitamin regulation is of particular significance in cystic fibrosis.
List of vitamins
Each vitamin is typically used in multiple reactions and, therefore, most have multiple functions.
|Vitamin generic descriptor name||Vitamer chemical name(s) (list not complete)||Solubility||Recommended dietary allowances
(male, age 19–70)
|Deficiency disease||Upper Intake Level
|Fat||900 µg||Night-blindness and
|3,000 µg||Hypervitaminosis A|
|Vitamin B1||Thiamine||Water||1.2 mg||Beriberi||N/D||Rare hypersensitive reactions resembling anaphylactic shock-- injection only;
|Vitamin B2||Riboflavin||Water||1.3 mg||Ariboflavinosis||N/D||?|
|Vitamin B3||Niacin, niacinamide||Water||16.0 mg||Pellagra||35.0 mg||Liver damage (doses > 2g/day) and other problems|
|Vitamin B5||Pantothenic acid||Water||5.0 mg||Paresthesia||N/D||?|
|Vitamin B6||Pyridoxine, pyridoxamine, pyridoxal||Water||1.3-1.7 mg||Anaemia||100 mg||Impairment of proprioception, nerve damage (doses > 100 mg/day)|
|Vitamin B7||Biotin||Water||30.0 µg||Dermatitis, enteritis||N/D||?|
|Vitamin B9||Folic acid, folinic acid||Water||400 µg||Deficiency during pregnancy is associated with birth defects, such as neural tube defects||1,000 µg||? Possible decrease in seizure threshold|
|Vitamin B12||Cyanocobalamin, hydroxycobalamin, methylcobalamin||Water||2.4 µg||Megaloblastic anaemia||N/D||No known toxicity|
|Vitamin C||Ascorbic acid||Water||90.0 mg||Scurvy||2,000 mg||Vitamin C megadosage|
|Vitamin D||Ergocalciferol, cholecalciferol||Fat||5.0 µg-10 µg||Rickets and Osteomalacia||50 µg||Hypervitaminosis D|
|Vitamin E||Tocopherols, tocotrienols||Fat||15.0 mg||Deficiency is very rare; mild hemolytic anemia in newborn infants.||1,000 mg||Increased congestive heart failure seen in one large randomized study.|
|Vitamin K||phylloquinone, menaquinones||Fat||120 µg||Bleeding diathesis||N/D||Increases coagulation in patients taking warfarin.|
In nutrition and diseases
Vitamins are essential for the normal growth and development of a multicellular organism. Using the genetic blueprint inherited from its parents, a fetus begins to develop, at the moment of conception, from the nutrients it absorbs. It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle. If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. Even minor deficiencies may cause permanent damage.
For the most part, vitamins are obtained with food, but a few are obtained by other means. For example, microorganisms in the intestine—commonly known as "gut flora"—produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Humans can produce some vitamins from precursors they consume. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.
Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.
Deficiencies of vitamins are classified as either primary or secondary. A primary deficiency occurs when an organism does not get enough of the vitamin in its food. A secondary deficiency may be due to an underlying disorder that prevents or limits the absorption or use of the vitamin, due to a “lifestyle factor”, such as smoking, excessive alcohol consumption, or the use of medications that interfere with the absorption or use of the vitamin. People who eat a varied diet are unlikely to develop a severe primary vitamin deficiency. In contrast, restrictive diets have the potential to cause prolonged vitamin deficits, which may result in often painful and potentially deadly diseases.
Because human bodies do not store most vitamins, humans must consume them regularly to avoid deficiency. Human bodily stores for different vitamins vary widely; vitamins A, D, and B12 are stored in significant amounts in the human body, mainly in the liver, and an adult human's diet may be deficient in vitamins A and B12 for many months before developing a deficiency condition. Vitamin B3 is not stored in the human body in significant amounts, so stores may only last a couple of weeks.
Well-known human vitamin deficiencies involve thiamine (beriberi), niacin (pellagra), vitamin C (scurvy) and vitamin D (rickets). In much of the developed world, such deficiencies are rare; this is due to (1) an adequate supply of food; and (2) the addition of vitamins and minerals to common foods, often called fortification.
Some evidence also suggests that there is a link between vitamin deficiency and mental disorders.
Side effects and overdose
In large doses, some vitamins have documented side effects that tend to be more severe with a larger dosage. The likelihood of consuming too much of any vitamin from food is remote, but overdosing from vitamin supplementation does occur. At high enough dosages some vitamins cause side effects such as nausea, diarrhea, and vomiting.
When side effects emerge, recovery is often accomplished by reducing the dosage. The concentrations of vitamins an individual can tolerate vary widely, and appear to be related to age and state of health. In the United States, overdose exposure to all formulations of vitamins was reported by 62,562 individuals in 2004 (nearly 80% of these exposures were in children under the age of 6), leading to 53 "major" life-threatening outcomes and 3 deaths;a small number in comparison to the 19,250 people who died of unintentional poisoning of all kinds in the U.S. in the same year (2004).
Dietary supplements, often containing vitamins, are used to ensure that adequate amounts of nutrients are obtained on a daily basis, if optimal amounts of the nutrients cannot be obtained through a varied diet. Scientific evidence supporting the benefits of some dietary supplements is well established for certain health conditions, but others need further study. A meta-analysis in 2006 suggested that Vitamin A and E supplements not only provide no tangible health benefits for generally healthy individuals, but may actually increase mortality, although two large studies included in the analysis involved smokers, for which it was already known that beta-carotene supplements can be harmful.
In the United States, advertising for dietary supplements is required to include a disclaimer that the product is not intended to treat, diagnose, mitigate, prevent, or cure disease, and that any health claims have not been evaluated by the Food and Drug Administration. In some cases, dietary supplements may have unwanted effects, especially if taken before surgery, with other dietary supplements or medicines, or if the person taking them has certain health conditions. Vitamin supplements may also contain levels of vitamins many times higher, and in different forms, than one may ingest through food.
Intake of excessive quantities can cause vitamin poisoning, often due to overdose of Vitamin A and Vitamin D (The most common poisoning with multinutrient supplement pills does not involve a vitamin, but is rather due to the mineral iron). Due to toxicity, most common vitamins have recommended upper daily intake amounts.
Since 2005, suppliers have distinguished their products as either Medical Grade or Pharmeceutical Grade products. Both of these classifications indicate products that are manufactured to be easily absorbed by the body. Normal vitamin manufacturing is not regulated in the United States to the same standards as are medicinal pharmaceuticals, although U.S. vitamins which are manufactured for food consumption by humans or animals must be manufactured to Food Chemicals Codex (FCC), grade, commonly called "food grade".
Governmental regulation of vitamin supplements
Most countries place dietary supplements in a special category under the general umbrella of foods, not drugs. This necessitates that the manufacturer, and not the government, be responsible for ensuring that its dietary supplement products are safe before they are marketed. Unlike drug products, which must explicitly be proven safe and effective for their intended use before marketing, there are often no provisions to "approve" dietary supplements for safety or effectiveness before they reach the consumer. Also unlike drug products, manufacturers and distributors of dietary supplements are not generally required to report any claims of injuries or illnesses that may be related to the use of their products.
Names in current and previous nomenclatures
The reason the set of vitamins seems to skip directly from E to K is that the vitamins corresponding to "letters" F-J were either reclassified over time, discarded as false leads, or renamed because of their relationship to "vitamin B", which became a "complex" of vitamins. The German-speaking scientists who isolated and described vitamin K (in addition to naming it as such) did so because the vitamin is intimately involved in the Koagulation of blood following wounding. At the time, most (but not all) of the letters from F through to J were already designated, so the use of the letter K was considered quite reasonable.
The following table lists chemicals that had previously been classified as vitamins, as well as the earlier names of vitamins that later became part of the B-complex:
|Previous name||Chemical name||Reason for name change|
|Vitamin B4||Adenine||DNA metabolite|
|Vitamin B8||Adenylic acid||DNA metabolite|
|Vitamin F||Essential fatty acids||Needed in large quantities (does|
not fit the definition of a vitamin).
|Vitamin G||Riboflavin||Reclassified as Vitamin B2|
|Vitamin H||Biotin||Reclassified as Vitamin B7|
|Vitamin J||Catechol, Flavin||Protein metabolite|
|Vitamin L1||Anthranilic acid||Protein metabolite|
|Vitamin L2||Adenylthiomethylpentose||RNA metabolite|
|Vitamin M||Folic acid||Reclassified as Vitamin B9|
|Vitamin O||Carnitine||Protein metabolite|
|Vitamin P||Flavonoids||No longer classified as a vitamin|
|Vitamin PP||Niacin||Reclassified as Vitamin B3|
|Vitamin U||S-Methylmethionine||Protein metabolite|
- Dietary supplement
- Fat soluble vitamins
- Illnesses related to poor nutrition
- Megavitamin therapy
- Nicotinic acid
- Orthomolecular medicine
- Vitamin poisoning (overdose)
- Vitimin therapy
- Lieberman, S, Bruning, N (1990). The Real Vitamin & Mineral Book. NY: Avery Group, 3.
- vitamin - definition of vitamin by the Free Online Dictionary, Thesaurus and Encyclopedia
- vitamer: Definition and Much More from Answers.com. www.answers.com. URL accessed on 2008-06-16.
- Maton, Anthea; Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright (1993). Human Biology and Health, Englewood Cliffs, New Jersey, USA: Prentice Hall.
- Accessed Jan 4, 2008
- Bolander FF (2006). Vitamins: not just for enzymes. Curr Opin Investig Drugs 7 (10): 912–5.
- Kirk-Othmer (1984). Encyclopedia of Chemical Technology Third Edition. NY: John Wiley and Sons, Vol. 24:104.
- Cite error: Invalid
<ref>tag; no text was provided for refs named
- 1929 Nobel lecture
- Tokyo Kagaku Kaishi: (1911)
- Funk, C. and H. E. Dubin. The Vitamines. Baltimore: Williams and Wilkins Company, 1922.
- Bellis, Mary. Vitamins - Production Methods The History of the Vitamins. Retrieved 1 February 2005.
- Fukuwatari T, Shibata K (June 2008). Urinary water-soluble vitamins and their metabolite contents as nutritional markers for evaluating vitamin intakes in young Japanese women. J. Nutr. Sci. Vitaminol. 54 (3): 223–9.
- Water-Soluble Vitamins. URL accessed on 2008-12-07.
- Said HM, Mohammed ZM (March 2006). Intestinal absorption of water-soluble vitamins: an update. Curr. Opin. Gastroenterol. 22 (2): 140–6.
- Maqbool A, Stallings VA (November 2008). Update on fat-soluble vitamins in cystic fibrosis. Curr Opin Pulm Med 14 (6): 574–81.
- Kutsky, R.J. (1973). Handbook of Vitamins and Hormones. New York:Van Nostrand Reinhold.
- Dietary Reference Intakes: Vitamins The National Academies, 2001.
- Vitamin and Mineral Supplement Fact Sheets Vitamin A
- N/D= "Amount not determinable due to lack of data of adverse effects. Source of intake should be from food only to prevent high levels of intake"(see Dietary Reference Intakes: Vitamins).
- J.G. Hardman et al., eds., Goodman and Gilman's Pharmacological Basis of Therapeutics, 10th ed., p.992.
- Plain type indicates Adequate Intakes (A/I). "The AI is believed to cover the needs of all individuals, but a lack of data prevent being able to specify with confidence the percentage of individuals covered by this intake" (see Dietary Reference Intakes: Vitamins).
- Vitamin and Mineral Supplement Fact Sheets Vitamin B6
- Vitamin and Mineral Supplement Fact Sheets Vitamin B12
- Value represents suggested intake without adequate sunlight exposure (see Dietary Reference Intakes: Vitamins).
- The Merck Manual: Nutritional Disorders: Vitamin Introduction Please select specific vitamins from the list at the top of the page.
- Rohde LE, de Assis MC, Rabelo ER (January 2007). Dietary vitamin K intake and anticoagulation in elderly patients. Curr Opin Clin Nutr Metab Care 10 (1): 1–5.
- Dr. Leonid A. Gavrilov, Pieces of the Puzzle: Aging Research Today and Tomorrow
- Lakhan SE; Vieira KF. Nutritional therapies for mental disorders. Nutrition Journal 2008;7(2).
- Institute of Medicine. Food and Nutrition Board. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. National Academy Press, Washington, DC, 2001.
- Healthier Kids Section: What to take and how to take it.
- 2004 Annual Report of the American Association of Poison Control Centers Toxic Exposure Surveillance System.
- National Center for Health Statistics
- Use and Safety of Dietary Supplements NIH office of Dietary Supplements.
- Bjelakovic G, et al (2007). Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis. JAMA 297 (8): 842–57.. See also the letter to JAMA by Philip Taylor and Sanford Dawsey and the reply by the authors of the original paper.
- Jane Higdon Vitamin E recommendations at Linus Pauling Institute's Micronutrient Information Center
- Overview of Dietary Supplements
- Illnesses and Injuries Associated with the Use of Selected Dietary Supplements U. S. FDA Center for Food Safety and Applied Nutrition
- Every Vitamin Page All Vitamins and Pseudo-Vitamins. Compiled by David Bennett.
- Vitamins and minerals - names and facts
- Michael W. Davidson (2004) Anthranilic Acid (Vitamin L) Florida State University. Accessed 20-02-07
- USDA RDA chart in PDF format
- Health Canada Dietary Reference Intakes Reference Chart for Vitamins
- NIH Office of Dietary Supplements: Fact Sheets
- NIH Office of Dietary Supplements. Dietary Supplements: Background Information
|All B vitamins | All D vitamins|
|Retinol (A) | Thiamine (B1) | Riboflavin (B2) | Niacin (B3) | Pantothenic acid (B5) | Pyridoxine (B6) | Biotin (B7) | Folic acid (B9) | Cyanocobalamin (B12) | Ascorbic acid (C) | Ergocalciferol (D2) | Cholecalciferol (D3) | Tocopherol (E) | Naphthoquinone (K)|
Nutritional pathology (E40-68, 260-269)
Obesity - Hypervitaminosis A - Hypervitaminosis D
Retinol (Vitamin A) •
B vitamins: Thiamine (B1) •
Pantothenic acid (B5)•
Folic acid (B9) •
Cyanocobalamin (B12) •
Ascorbic acid (Vitamin C) •
Ergocalciferol and Cholecalciferol (Vitamin D) •
Tocopherol (Vitamin E) •
Naphthoquinone (Vitamin K) •
Other Common Ingredients
Chondroitin sulfate •
Cod liver oil •
Copper gluconate •
Dietary fiber •
Elemental calcium •
Fish oil •
Folic acid •
Iron supplements •
Japanese Honeysuckle •
Krill oil •
Linseed oil •
Red yeast rice •
Royal jelly •
Saw Palmetto •
Spirulina (dietary supplement) •
Zinc gluconate •
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